task: add USE_REACT feature toggle.

As frontend is developed independently from backend, we should have a toggle to keep the components
switched off until we have API.

Part of #1328

[skip ci]

Author: php-coder

src/main/java/ru/mystamps/web/support/togglz/Features.java

@@ -31,6 +31,9 @@ public enum Features implements Feature {
 	@Label("Use a country microservice for the country-related functions")
 	USE_COUNTRY_MICROSERVICE,
 
+	@Label("Use React components instead of server rendered HTML")
+	USE_REACT,
+	
 	@Label("/site/index: feature to check that Togglz works")
 	ALWAYS_DISABLED,